As illustrated in FIG. 42, a steering apparatus for an automobile applies a steering angle to the front wheels by transmitting rotation of the steering wheel 1 to an input shaft 3 of a steering gear unit 2, and pushing or pulling a pair of left and right tie rods 4 as the input shaft 3 rotates. The steering wheel 1 is inserted in the axial direction through a cylindrical shaped steering column 6, and is supported by and fastened to this steering column 6 so as to be able to rotate freely. The front-end section of a steering shaft 5 is connected to the rear-end section of an intermediate shaft 8 by way of a universal joint 7, and the front end of this intermediate shaft 8 is connected to the input shaft 3 by way of a separate universal joint 9. The intermediate shaft 8 is constructed so as to be able to transmit torque, as well as to be able to contract along the entire length due to an impact load, so that during a primary collision of collision accident when an automobile collides with another automobile or the like, regardless of displacement toward the rear of the steering gear unit 2, it is prevented that the steering wheel 1 displaces toward the rear by way of the steering shaft 5 so as to shove or press against the body of the operator.
During a collision accident, a secondary collision occurs after the primary collision when the body of the operator collides with the steering wheel 1. In order to lessen the impact that is applied to the body of the operator during this secondary collision, the steering column 6 is supported by way of a locking capsule 11 and bolts or studs by a vehicle-side bracket 10 that is fastened to the vehicle so that when a large force is applied in the forward direction, the steering column 6 drops away from the vehicle-side bracket 10. Construction for supporting this steering column 6 by the vehicle-side bracket 10 is conventionally known. An example of conventional support construction is disclosed in JP2010-13010(A), and will be explained using FIG. 43 to FIG. 45.
In the construction illustrated in FIG. 43, a tilt mechanism is assembled which allows height adjustment of the steering wheel 1 (see FIG. 42) that is fastened to the portion on the rear-end section of the steering shaft 5 that protruded toward the rear of the steering column 6a. Therefore, the middle section of the steering column 6a is supported by a column-side bracket 13 by way of an adjustment rod 14, and this column-side bracket 13 is supported by the vehicle-side bracket 10 (see FIG. 42) so as to drop away when a large force is applied in the forward direction as illustrated by the arrow in FIG. 43. The column-side bracket 13 is integrally formed by bending a metal plate such as steel plate and comprises a pair of left and right support plate sections 15 that are provided in the up-down direction, a pair of installation plate sections 16 that are provided so as to protrude toward both sides of the steering column 6a from the top end section of the support plate sections 15, and a connecting section (omitted from the figures) that connects together the bottom end edges of the pair of support plate sections 15.
Locking notches 17 are provided in the pair of installation plate sections 16 so as to be open on the rear-end edges of the installation plate sections 16. The shape of these locking notches 17 is a substantially trapezoidal shape wherein the width dimension becomes smaller going toward the front (bottom side). Locking capsules 11 are assembled on the inside of these locking notches 17. These locking capsules 11 are formed by injection molding using synthetic resin, or die-casting using a light alloy, and each locking capsule 17 has locking grooves 18 on the left and right sides. The space between the bottoms of the grooves of these locking grooves 18, in order to match the width of the locking notches 17, becomes narrow going toward the front. In other words, the locking grooves 18 become deeper toward the front.
These locking capsules 11 each are supported by one of the pair of installation plate sections 16 by engaging the locking grooves 18 thereof with portions of the installation plate section 16 located on both sides of the locking notches 17. With small though holes (omitted in the drawings) that are formed in the portions of the installation plate section 16 located on both sides of the locking notches 17 aligned with small through holes 19 that are formed in the locking capsules 11, synthetic resin locking pins that are connecting members are formed by injection molding so as to span through these small through holes. In this state, the pair of locking capsules 11 are supported by the pair of installation plate sections 16 so that they drop away toward the rear only when a large impact load is applied.
As illustrated in FIG. 42, by inserting bolts or studs 12 from the bottom through a through hole 20 that is formed in the center section of the locking capsules 11, the pair of locking capsules 11 are supported by and fastened to the vehicle-side bracket 10. In order for this, screw holes for screwing the bolts or studs 12 into are formed directly in the vehicle-side bracket 10 or nuts are fastened by welding or the like to surface thereof. Each pair of a locking capsule 11 and installation plate section 16 are joined together with somewhat large force and rigidity by engagement of the portions located on both sides of the locking notches 17 and the locking grooves 18, and by the synthetic resin locking pins that span through the small through holes 19. Therefore, during normal operation, the column-side bracket 13 is firmly supported by the vehicle body.
When a strong force in the forward direction is applied to the steering column 6a from the steering wheel 1 during a secondary collision that accompanies a collision accident, the locking pins inside the small through holes 19 shear and the pair of locking capsules 11 come out toward the rear from the pair of locking notches 17. In other words, the installation plate sections 16 displace in the forward direction with the locking capsules remaining in position as is. This allows the steering wheel 1 to displace in the forward direction, which lessens the impact that is applied to the body of the operator who collides with the steering wheel 1.
In the case of the construction illustrated in FIG. 43 to FIG. 45, the column-side bracket 14 is supported at two locations on both the left and right side by the vehicle-side bracket 10. In the case of this construction, releasing the engagement of the pair of left and right engagement section at the same time during a secondary collision is important from the aspect of allowing the steering wheel 1 to displace in smoothly in the forward direction with no inclination. However, tuning in order that engagement of these engagement sections is released at the same time is affected by resistance such as the friction resistance and shear resistance against the release of these engagement sections, and is also affected by unbalance on the left and right of the inertia mass of the portion that displaces in the forward direction together with the steering column 6a, so this tuning work takes time. JP51-121929(A) discloses a structure in which an engagement section between the vehicle-side bracket and locking capsule is provided at only one location in the center section in the width direction in order that the steering column breaks stably away in the forward direction during a secondary collision.
In the case of comprising a tilt mechanism and/or a telescoping mechanism, in order to increase the holding strength for supporting the steering wheel 1 in the adjusted position, JP2007-69821(A) and JP2008-100597(A) disclose a structure in which a friction plate unit is held between the inside surfaces of the pair of support plate sections 15 and the outside surfaces of a pair of supported plate sections on the steering column 6a side in order to increase the friction surface area between the surfaces. More specifically, this friction plate unit comprises one or more first friction plates in which long holes are formed that are aligned with long holes in the up-down direction that are formed in the support plate sections 15 in order for the tilt mechanism, and one or more second friction plates in which long holes are formed that are aligned with long holes in the forward-backward that are formed in the supported plate section on the steering column 6a side for the telescoping mechanism, with these friction plates overlapping each other.